core-lightning/doc/schemas/lightning-fundpsbt.json

{
  "$schema": "../rpc-schema-draft.json",
  "type": "object",
  "rpc": "fundpsbt",
  "title": "Command to populate PSBT inputs from the wallet",
  "description": [
    "`fundpsbt` is a low-level RPC command which creates a PSBT using unreserved inputs in the wallet, optionally reserving them as well."
  ],
  "request": {
    "required": [
      "satoshi",
      "feerate",
      "startweight"
    ],
    "additionalProperties": false,
    "properties": {
      "satoshi": {
        "type": "sat_or_all",
        "description": [
          "The minimum satoshi value of the output(s) needed (or the string `all` meaning use all unreserved inputs). If a value, it can be a whole number, a whole number ending in *sat*, a whole number ending in *000msat*, or a number with 1 to 8 decimal places ending in *btc*."
        ]
      },
      "feerate": {
        "type": "feerate",
        "description": [
          "Used for the transaction as initial feerate."
        ],
        "default": "*normal*"
      },
      "startweight": {
        "type": "u32",
        "description": [
          "The weight of the transaction before *fundpsbt* has added any inputs."
        ]
      },
      "minconf": {
        "type": "u32",
        "description": [
          "The minimum number of confirmations that used outputs should have."
        ],
        "default": "1"
      },
      "reserve": {
        "type": "u32",
        "description": [
          "If not zero, then *reserveinputs* is called (successfully, with *exclusive* true) on the returned PSBT for this number of blocks."
        ],
        "default": "72 blocks"
      },
      "locktime": {
        "type": "u32",
        "description": [
          "The locktime of the transaction. if not set, it is set to a recent block height."
        ]
      },
      "min_witness_weight": {
        "type": "u32",
        "description": [
          "Minimum weight to use for a UTXO's witness. If the actual witness weight is greater than the provided minimum, the actual witness weight will be used."
        ]
      },
      "excess_as_change": {
        "type": "boolean",
        "description": [
          "Flag to add a change output for the excess sats."
        ]
      },
      "nonwrapped": {
        "added": "v23.02",
        "type": "boolean",
        "description": [
          "To signal to filter out any p2sh-wrapped inputs from funding this PSBT."
        ]
      },
      "opening_anchor_channel": {
        "added": "v23.08",
        "type": "boolean",
        "description": [
          "To signel that it needs emergency reserve for anchors so that we can lowball our commitment tx fees, and min-emergency-msat for reserving some sats for closing anchor channels."
        ]
      }
    }
  },
  "response": {
    "required": [
      "psbt",
      "feerate_per_kw",
      "estimated_final_weight",
      "excess_msat"
    ],
    "additionalProperties": false,
    "properties": {
      "psbt": {
        "type": "string",
        "description": [
          "Unsigned PSBT which fulfills the parameters given."
        ]
      },
      "feerate_per_kw": {
        "type": "u32",
        "description": [
          "The feerate used to create the PSBT, in satoshis-per-kiloweight."
        ]
      },
      "estimated_final_weight": {
        "type": "u32",
        "description": [
          "The estimated weight of the transaction once fully signed."
        ]
      },
      "excess_msat": {
        "type": "msat",
        "description": [
          "The amount above *satoshi* which is available. This could be zero, or dust; it will be zero if *change_outnum* is also returned."
        ]
      },
      "change_outnum": {
        "type": "u32",
        "description": [
          "The 0-based output number where change was placed (only if parameter *excess_as_change* was true and there was sufficient funds)."
        ]
      },
      "reservations": {
        "type": "array",
        "description": [
          "If *reserve* was true or a non-zero number, just as per lightning- reserveinputs(7)."
        ],
        "items": {
          "type": "object",
          "required": [
            "txid",
            "vout",
            "was_reserved",
            "reserved",
            "reserved_to_block"
          ],
          "additionalProperties": false,
          "properties": {
            "txid": {
              "type": "txid",
              "description": [
                "The txid of the transaction."
              ]
            },
            "vout": {
              "type": "u32",
              "description": [
                "The 0-based output number."
              ]
            },
            "was_reserved": {
              "type": "boolean",
              "enum": [
                false
              ],
              "description": [
                "Whether this output was previously reserved."
              ]
            },
            "reserved": {
              "type": "boolean",
              "enum": [
                true
              ],
              "description": [
                "Whether this output is now reserved."
              ]
            },
            "reserved_to_block": {
              "type": "u32",
              "description": [
                "The blockheight the reservation will expire."
              ]
            }
          }
        }
      }
    },
    "post_return_value_notes": [
      "If *excess_as_change* is true and the excess is enough to cover an additional output above the `dust_limit`, then an output is added to the PSBT for the excess amount. The *excess_msat* will be zero. A *change_outnum* will be returned with the index of the change output."
    ]
  },
  "usage": [
    "Let's assume the caller is trying to produce a 100,000 satoshi output.",
    "",
    "First, the caller estimates the weight of the core (typically 42) and known outputs of the transaction (typically (9 + scriptlen) * 4). For a simple P2WPKH it's a 22 byte scriptpubkey, so that's 124 weight.",
    "",
    "It calls \"*fundpsbt* 100000sat slow 166\", which succeeds, and returns the *psbt* and *feerate_per_kw* it used, the *estimated_final_weight* and any *excess_msat*.",
    "",
    "If *excess_msat* is greater than the cost of adding a change output, the caller adds a change output randomly to position 0 or 1 in the PSBT. Say *feerate_per_kw* is 253, and the change output is a P2WPKH (weight 124), the cost is around 31 sats. With the dust limit disallowing payments below 546 satoshis, we would only create a change output if *excess_msat* was greater or equal to 31 + 546."
  ],
  "errors": [
    "On error the returned object will contain `code` and `message` properties, with `code` being one of the following:",
    "",
    "- -32602: If the given parameters are wrong.",
    "- -1: Catchall nonspecific error.",
    "- 301: Insufficient UTXOs to meet *satoshi* value."
  ],
  "author": [
    "Rusty Russell <<rusty@rustcorp.com.au>> is mainly responsible."
  ],
  "see_also": [
    "lightning-utxopsbt(7)",
    "lightning-reserveinputs(7)",
    "lightning-unreserveinputs(7)"
  ],
  "resources": [
    "Main web site: <https://github.com/ElementsProject/lightning>"
  ],
  "examples": [
    {
      "request": {
        "id": "example:fundpsbt#1",
        "method": "fundpsbt",
        "params": {
          "satoshi": 1000000,
          "feerate": "253perkw",
          "startweight": 250,
          "reserve": 0
        }
      },
      "response": {
        "psbt": "cHNidP8BAF4CAAAAAZiQf/mEs4NcFFfD4K8xauOgSpbz/xeetoXVWAPCI0h6AQAAAAD9////AahhAAAAAAAAIlEg+3d9jpNmK0getyg5W+Mp31CPIRDKcJg/mZs/uaVrQ+GZAAAAAAEAiQIAAAABswU80whDZOoIHS/lfyxwmHh5USHBwbcjWHaJ9/XU+78BAAAAAP3///8CgIQeAAAAAAAiACDJvFwGPK7796bHgUQHtWJ7T4GotW7L6TLGgvnLrA0Z32INzQsAAAAAIlEgyRg+3pEh88b9FJiCLEenYCcyJ2ackJUIhDusW72BP2iYAAAAAQErYg3NCwAAAAAiUSDJGD7ekSHzxv0UmIIsR6dgJzInZpyQlQiEO6xbvYE/aAAA",
        "feerate_per_kw": 253,
        "estimated_final_weight": 693,
        "excess_msat": 196962507000,
        "change_outnum": 0
      }
    },
    {
      "request": {
        "id": "example:fundpsbt#2",
        "method": "fundpsbt",
        "params": {
          "satoshi": 500000,
          "feerate": "urgent",
          "startweight": 166,
          "reserve": 0,
          "excess_as_change": true,
          "min_witness_weight": 110
        }
      },
      "response": {
        "psbt": "cHNidP8BAF4CAAAAAZiQf/mEs4NcFFfD4K8xauOgSpbz/xeetoXVWAPCI0h6AQAAAAD9////AfZRxQsAAAAAIlEg21kTTo7K2doCG6F2JqgaDjc1kRCrH7AL08oPVVJhuE+ZAAAAAAEAiQIAAAABswU80whDZOoIHS/lfyxwmHh5USHBwbcjWHaJ9/XU+78BAAAAAP3///8CgIQeAAAAAAAiACDJvFwGPK7796bHgUQHtWJ7T4GotW7L6TLGgvnLrA0Z32INzQsAAAAAIlEgyRg+3pEh88b9FJiCLEenYCcyJ2ackJUIhDusW72BP2iYAAAAAQErYg3NCwAAAAAiUSDJGD7ekSHzxv0UmIIsR6dgJzInZpyQlQiEO6xbvYE/aAAA",
        "feerate_per_kw": 11000,
        "estimated_final_weight": 612,
        "excess_msat": 0,
        "change_outnum": 0
      }
    }
  ]
}